There are known various compositions having a disperse phase dispersed in a continuous phase, including emulsions having a disperse phase liquid dispersed in a continuous phase liquid, and microbubble compositions having a disperse phase gas dispersed in a continuous phase liquid. Conventional emulsions have been prepared by adding a liquid that is to serve as a disperse phase, together with an emulsifying agent such as a surfactant, to a liquid that is to serve as a continuous phase, to give a liquid mixture and mechanically stirring the liquid mixture to micronize the disperse phase.
As exemplary techniques for producing an emulsion more efficiently, there are disclosed in Patent Literatures 1-3 methods for causing an oil-soluble liquid and a water-soluble liquid to permeate a porous membrane. To be specific, Patent Literature 1 discloses that in order to obtain an emulsion having a small average particle size, emulsion production should be done by using a porous membrane having a small pore size and decreasing a membrane permeation rate (par. [0021]). This literature also discloses in Example 1 an example where an emulsion was produced using a porous membrane having an average pore size of 2.7 μm at a membrane permeation rate of 350 cc/3140 mm2 min. This membrane permeation rate can be converted to 6 m3/m2h.
Patent Literature 2 discloses an example where an emulsion containing 12.5% by mass of a disperse phase was produced using a porous membrane having an average pore size of 5 μm at a membrane permeation rate of 43.3 mL/25 cm2 sec (Example 12). This membrane permeation rate can be converted to 60 m3/m2h.
Patent Literature 3 discloses an example where an oil-soluble liquid and a water-soluble liquid were allowed to permeate a porous membrane having an average pore size of 5.3 μm and an effective area of 3140 mm2 at a membrane permeation rate of 2 L/min, to thereby produce an emulsion containing 40% by volume of a disperse phase (Example 3). This membrane permeation rate can be converted to 38 m3/m2h.
Non-patent Literature 1 discloses examples where emulsions each containing a disperse phase at a concentration of 1-20% by volume were produced using porous membranes having an average pore size of 7.6-20.3 μm at a membrane permeation rate of 80-240 m3/m2h (Non-patent Literature 1, FIG. 8).